fix: properly mock Docker container image in tests

dashboard/backend/tests/conftest.py

@@ -101,11 +101,19 @@ def mock_docker_client():
     """Mock Docker client for testing."""
     client = Mock()
 
+    # Mock container image
+    mock_image = Mock()
+    mock_image.tags = ["test-image:latest"]
+    mock_image.id = "sha256:abc123def456"
+
     # Mock container
     container = Mock()
     container.id = "abc123"
+    container.short_id = "abc123"
     container.name = "test-container"
     container.status = "running"
+    container.image = mock_image
+    container.ports = {"80/tcp": [{"HostPort": "8080"}]}
     container.attrs = {
         "State": {"Health": {"Status": "healthy"}},
         "Config": {"Image": "test-image:latest"}